The aim of this project is to evaluate hemorheological parameters associated with stroke due to thromboembolic disease. Cerebral ischemic events will be classified using a variety of clinical characteristics. Patients with cerebral ischemia will be studied with respect to blood and plasma viscosity, red cell aggregation, and erythrocyte deformability. The relationship between these parameters and both platelet activation and hyperglycemia will be explored. It is hypothesized that: 1) Specific subsets of cerebral ischemia are most likely to be associated with hemorheological alterations; and 2) The risk of hyperglycemia in stroke and the finding of increased platelet activation in cerebral ischemia are related to underlying hemorheological abnormalities. One hundred fifty patients will be entered into this study over a three-year period. These patients will be characterized using neurological and hemorheological parameters. The stroke subsets will include the following: 1) Etiology, consisting of large vessel occlusive disease (including carotid versus vertebral-basilar insufficiency and embolic versus flow-related symptoms), lacunar disease, cardiogenic stroke, and stroke of unknown origin; 2) Progressive versus non-progressive stroke; 3) Diabetic versus non-diabetic patients; 4) Severe versus non-severe neurological deficit and good versus poor outcome at 3 months; and 5) Platelet activation, measured by plasma beta-thromboglobulin, normal or increased. Hemorheological studies will consist of the following: 1) Viscosity, both whole blood and plasma, using a cone-plate viscometer; 2) Red cell aggregation measured by zeta sedimentation ratio and aggregation half-time and aggregation index; and 3) Erythrocyte deformability using the technique of centrifugal deformation. The statistical analysis will attempt to delineate which subsets of stroke patients are more likely to be associated with hemorheological alterations which could then be manipulated during the course of therapeutic intervention.